The study found that a natural membrane from the placenta (amnion‑chorion) contains four antimicrobial proteins, including the peptide LL‑37. When tested alone, each protein only weakly killed the oral bacterium Streptococcus gordonii, but together they killed the bacteria much more effectively, showing a clear synergy. This suggests that combinations of such proteins work better than any single one for preventing bacterial growth on medical membranes.

The human-derived amnion-chorion membrane (ACM) has endogenous antimicrobial properties, which are important for preventing the colonization and survival of oral bacteria on exposed membranes. This project aimed to decipher the underlying mechanism by identifying the components of ACM that confer antibacterial properties. In addition, the antimicrobial efficacy of these identified components on oral bacteria was assessed. Four antimicrobial proteins, histone H2A/H2B, cathelicidin LL-37, lactoferrin, and lysozyme, were identified via mass spectrometry in ACM. These proteins were then assessed for their efficacy in killing <i>Streptococcus gordonii</i> Challis. Log-phased bacterial cells were cultured with the commercially available proteins that were identified in ACM, either individually or in combination, at different concentrations. After incubation for 8 or 24 hours, the bacteria were stained with a live/dead viability kit and analyzed via confocal microscopy. The combination of these proteins effectively killed <i>S. gordonii</i> in a dose-dependent fashion after 8 or 24 hours of incubation. When each protein was tested individually, it killed <i>S. gordonii</i> at a much lower efficacy relative to the combinations. The synergistic effects of the antimicrobial protein combinations were also observed in both the viable cell count recovery and minimum inhibitory concentration assays. By shedding light on the mechanisms in the ACM's antimicrobial property, this study may raise more awareness of the potential benefit of utilization of a membrane with endogenous antimicrobial properties in regeneration surgeries.